1. Field of the Invention
The present invention relates to mobile communication technologies, and more particularly, to a method for efficiently transmitting and receiving control information through a Physical Downlink Control Channel (PDCCH).
2. Discussion of the Related Art
The following description can be applied to various mobile communication methods. However, a description will be given, particularly with reference to Third Generation Partnership Project Long Term Evolution (3GPP LTE) technologies.
3GPP LTE is a project for improving the UMTS mobile station standard to cope with future technology development in the Third Generation Partnership Project (3GPP). 3GPP LTE has evolved to Release 8 which is an improved version of the 3GPP standard.
In the 3GPP LTE communication system, various channels are defined for uplink and downlink in the physical layer used in actual signal transmission. For example, a Physical Uplink Shared Channel (PUSCH), a Physical Uplink Control Channel (PUCCH), and a Physical Random Access Channel (PRACH) are defined as uplink physical channels, and a Physical Downlink Shared Channel (PDSCH), a Physical Multicast Channel (PMCH), a Physical Broadcast Channel (PBCH), a Physical Control Format Indicator Channel (PCFICH), a Physical Downlink Control Channel (PDCCH), and a Physical Hybrid ARQ (HARQ) Indicator Channel (PHICH) are defined as downlink physical channels. In the following description, the word “physical” will be omitted for ease of explanation unless the omission causes confusing.
Among the various channels, the PDCCH serves to transmit scheduling allocation control information and other control information. In a cellular communication system in which one base station (or Node-B) controls a plurality of User Equipments (UEs) or (mobile stations), multiple UEs can receive control information through a PDCCH transmitted from the base station. Here, since there is a limit to the number of PDCCHs that the base station can transmit at once, the base station does not previously allocate different PDCCHs to each UE but transmits control information through an arbitrary PDCCH to an arbitrary UE at each time. Thus, the UE determines whether or not control information received through the PDCCH belongs to the UE based on a UE identifier included in the PDCCH. At each time, the UE performs decoding on each of a plurality of PDCCHs (for a plurality of possible PDCCH formats) and receives, when it is determined that the PDCCH corresponds to the UE, control information included in the PDCCH and operates according to the control information.
However, the number of combinations of PDCCH regions for transmission of control information may be great. Excessive UE processing performance may be required for the UE to decode all PDCCH regions. Accordingly, there is a need to limit PDCCH regions to be decoded by each UE to reduce the number of times the UE performs decoding and thus to reduce power consumption of the UE.